Device for signaling the presence of illuminating gas in inhabited premises



Oct. 31, 1939. G. MENOZZI 2,178.486

DEVICE FOR SIGNALING THE PRESENCE OF ILLUMINATING GAS IN INHABI'I'EDPREMISES Filed Aug. 29, 1956 Fz'y/ UNITED STATES PATENT OFFICE DEVICEFOR SIGNALING THE PRESENCE OF ILLUMINATING GAS 1N INHABITED PREM- ISISGiuseppe Menozzi, Messina, Italy Application August 29, 1936, Serial No.98,613 In Italy December 19, 1935 1 Claim.

It is known that there are devices for signaling the presence ofilluminating gas in inhabited premises founded on the attribute ofplatinum sponge of becoming heated in the presence of hy- 5 drogen andoxygen.

Generally, these devices consist of an ordinary mercury thermometer withan electric contact whose bulb is in contact with a platinum sponge; theheating of the sponge caused by the gas diffused in the room, inconsequence of eventual escapes, causes the mercury in the thermometriccolumn to rise until it establishes an electric contact, thus provokingthe closing of the alarm circuit. In other devices, instead, theordinary mercury thermometer is substituted by a type of differentialthermometer, actuated by gas or by electric contact, having one of itsbulbs in contact with a platinum sponge. None of the preceding devices,however, as far as is known, appears to be made according toexperimental data regarding the rising of temperature to which a pieceof platinum sponge might be subject in premises in which an escape ofgas occurs. This means, consequently, that in none of the said devicessuch working conditions occur, and that no device of the kind, as far asthe applicant is aware, has been practically realized.

The present invention is based on an experimental research aiming atestablishing the conditions for the heating of 'a platinum sponge, orother catalyzer of the kind, placed .in a room in which there occurs anescape of gas.

This research gives the following result:

As the ordinary illuminating gas consists essentiallyof a combination ofhydrogen and oxide of carbon and that the heating of the platinum spongeis due to the reaction 2H2+Oz=2H2O, it follows-that in ordinarydwellings the platinum sponge coming into contact with escaping gas gets40 heated by only a few degrees (not more than about ten) independentlyof the position which it occupies in the room, even when there occurs aconsiderable escape of gas, and this because the hydrogen contained inthe gas, owing to its very high coeflicient of diffusion spreads rapidlyall over theroom (and does not gather under the ceiling of the room, assome people erroneously believe) and also out of the room through theinevitable fissures of the doors and windows, reaching, however, in theroom a concentration limit given by the equilibrium which depends,besides on the entity of the escape, on the size of the room, and on thenumber and conditions of the doors and windows. In consequence of this,several hours after the gas escape has occurred, the concentration ofthe hydrogen is the same as that attained shortly after the beginning ofthe escape; while the concentration of the oxide of carbonium (which isthe poisonous constituent of the gas) increases continuously as timepasses by ii because, having a density equal to that of the air.

it spreads very slowly.

This is the reason why the devices already known do not attain thedesired object. In fact: in the case of devices containing ordinary mer-10 cury thermometers, it happens that as the latter are influenced bythe variations of the temperature in the room, which may even rise to 30degrees centigrade and upwards (taking into ac count the fact thatduring the winter the tem- 15 perature may fall considerably in thehours of the night, which are the more dangerous ones, compared with themaximum reached during the summer), it follows that for the functioningof the device in these conditions the platinum 20 sponge must produce inthe bulb of the thermometer a heat of over 30 degrees centigrade inorder to ensure such functioning at any hour during the day and night.

As regards devices provided with a differential 25 thermometer thefailure in functioning is due to the lack of knowledge of the lowconcentration limit attained by the hydrogen and, consequently, to thelack of knowledge of the maximum temperature which the platinum spongemay reach 30 in a room in which occurs an escape of gas. Consequently,in planning the differential thermometers used in the devices alreadyknown, no account is taken of the minimum sensitiveness required fortheir working. 35

Object of the present invention is to provide a device of a suff cientsensitiveness as will ensure the working of the alarm device in anydwelling room. To obtain this, it is assumed that the M heating of theplatinum sponge may be reduced to only 3 degrees centigrade" in verylarge rooms with numerous apertures so that the signaling device isconstituted of a differential thermometer worked by gas with electriccontact capable of closing an electric circuit whenever between its twobulbs there occurs a difference of temperature of 3 degrees centigrade,or more. a

In practice, with this device, in one room measuring meters 3 x 3 x 3,the closing of the 5g circuit occurs after a couple of minutes.

In the annexed drawing are illustrated, only by way of example andwithout limitation, two manners of realization of the thermometers andof the device referred to in the invention. so

Fig. 1 is an elevation of a thermometer used in one embodiment of theinvention.

Fig. 2 is a view. somewhat diagrammatic, of one embodiment of theinvention complete, the bulb covers being shown in section.

Fig. 3 is an elevation 01' another embodiment, the bulb covers beingshown in section.

A thermometer oi the kind (Fig. 1) is made of two glass bulbs A and Bconnected by means of a capillary tube C with two bubbles l and 2, inwhich is contained a drop of mercury 3.

Inbubbles I and 2 are soldered two platinum threads 4 and 5, of whichone 5 is in permanent contact with mercury 3; the other is meant to comeinto contact with the mercury only in consequence of the heating of bulbB. The two bulbs A and B contain air, or preferably hydrogen underordinary, or higher, pressure. When the two bulbs are at the sametemperature, the mercury assumes in the capillary tube the positionshown in the drawing (Fig. 1) and must retain it whatever be thetemperature of the room, provided it be the same in the two bulbs. Ifbulb B gets heated, the pressure of the gas contained therein increasesthus provoking a displacement of the mercury towards bulb A until therestoration of an equal pressure in the two bulbs.

The contact between the mercury and platinum thread 4 of bubble I may befixed in advance for a determined excess of temperature of bulb Brespect to bulb A. When an equal temperature has been re-established inthe two bulbs, the mercury will resume its primitive position.

The essential characteristics of this thermometer are therefore:

(1) Absolute indifference to the variations of the temperature of theroom.

(2) Closing of the electric contact whenever the temperature of one ofthe bulbs exceeds by a number of degrees fixed in advance thetemperature of the other bulb, whatever the temperature of the lattermay be.

(3) Possibility of fixing this number of degrees as small as may bedesired, the only obstacle to the moving of the drop of mercury beingreduced to the sole attrition with the casing and with the platinumthread 5.

Fig. 2 shows a form of execution of the device referred to in theinvention. A and B are the two bulbs of the thermometer; 'l is thecatalyzer of the reaction between hydrogen and oxygen in the shape of asmall cylinder in contact with bulb B; 6 is a small cylinder of the samedimensions as I but made of a substance having the same thermicconductiveness of small cylinder 1 but without having the same catalyticproperties; so that, in default of a gas escape, the variations in thetemperature of the room have the same influence in the two bulbs A andB. P are the batteries and C an alarm bell. (Other accessories, such asan automatic apparatus for closing the gas tap, or other signaling meansmay be added in the manner already known.)

When, owing to an escape of gas, hydrogen comes into contact withplatinum sponge I, the latter gets heated by a certain number of degreesthough the concentration of the hydrogen be very low, and being incontact with bulb B of the thermometer, it communicates such rise oftemperature to the gas contained therein, which dilates pressing themercury in the capillary tube so as to close the electric circuit whichactuates the alarm signal, or the protective apparatuses installed.

The thermometer is made in such a way (volume of the bulbs, diameter ofthe capillary tube, distance of the drop of mercury from platinum thread4, thickness and quality oi the glass, etc.) that the closing of theelectric circuit happens when the temperature of bulb B is by only 3degrees centigrade superior to that of bulb A; which, in a room of thesize 01 meters 3 x 3 x 3 and with three windows and adoor, (closed atthe time of the experiment), occurs after one minute from the completeopening of a common gas tap.

An improvement of this thermometer is represented in Fig. 3. In thisthermometer the two bubbles i and 2 of Fig. 1 have been suppressed; theplatinum threads of a sufliciently reduced thickness have been bothplaced on the same part and introduced into the capillary tube withoutany contact between each other and with their points on the same plane.The mercury drop has been reduced to two or three millimeters in length.

By this modification there has been obtained an increase ofsensitiveness in relation to the form represented in Fig. 1, as theresistance opposed to the motion of the drop of mercury has beenconsiderably reduced. Furthermore, the presence of platinum threads of asmall thickness ensures the following result: when, in consequence ofthe heating of bulb B, the mercury comes into contact with the twoplatinum threads causing the closing of the alarm circuit, an electriccurrent originates through the said threads which, being of a smalldiameter opportunely chosen (about millimeter 0.1), get heated andconsequently cause the heating of the gas of bulb A up to its reaching atemperature above that of the gas of bulb B. In consequence thereof, the

drop of mercury is repelled and determines the interruption of thecircuit, to resume once more contact with the platinum threads when,following upon a natural cooling down, the temperature of the gas inbulb A has become inferior to that of bulb B; and so on until thereremains in the room the presence of the illuminating gas. Thus theintermitting closing of the alarm circuit is obtained.

This intermittent closing does not impair anyhow the advantages of thedevice, because the action of the automatic apparatuses eventuallyintroduced in respect of the alarm bell, closing of the gas tap,lighting of the apartment, etc. is ensured by means of a relay operatedby the first closing of the circuit. The intermittent closing ensuresfurthermore the return to its place of the drop of mercury when thepresence of gas in the room ceases, and at the same time prevents that,in consequence of an eventual excessive heating of bulb B, the drop ofmercury be projected into bulb A.

The device thus constituted is wrapped in a layer of cotton-wool, or ofglass-wool which, besides ensuring its regular working, preserves itfrom dust and froni the dampness of the atmosphere. The whole is thenproperly closed in a metallic net placed on an insulating base.

Another improvement of the differential thermometer aforedescribed, asregards promptitude and sensitiveness, is obtained by substituting thetwo glass bulbs A and B with two bulbs made of thin silver plate.

What I claim and desire to secure by Letters Patent is:

A device for signaling the presence of illuminating gas in inhabitedpremises, comprising two axially aligned gas filled bulbs, a straightline capillary tube connecting said bulbs along their axes, a drop ofmercury in said tube normally balanced as to position by equal gaspressure in the two bulbs when both bulbs are at the same temperature,each-bulb being covered in like degree by covers having the same thermicconductivity, one of said covers having catalytic properties in excessof the other, and electric terminal wires projected into said capillarytube to cooperate with said mercury drop for the purpose of closing anelectric circuit upon a determined rise in the temperature of the bulbhaving the catalyzer above that of the surrounding atmosphere, saidwires entering said capillary tube at one end and both wires beingnormally out of contact with said mercury drop for purposes described.

GIUSEPJPE MENOZZI.

